Orifice valves are useful for control of flow of fluids, such as fluids produced from oil and gas wells and the like. Orifice valves, for example, are used for control of the rate of flow of well production fluids through a flow line. Often, such fluids contain abrasive materials, such as sand particles.
The rate of flow through an orifice valve is in part determined by the number and size of holes in both a stationary disk and a rotatable disk mounted across a fluid path in a valve body. The holes in the rotatable disk are positioned in various degrees of alignment with holes in the stationary disk by angular movement of the rotatable disk. The rotatable disk can be moved from a fully closed position for blocking flow through the valve to a fully open position for providing maximum flow through the valve.
Sometimes orifice valves have a severe erosion problem caused by the passage of abrasive fluids. Erosion results in a high frequency of valve replacement.
A major portion of the erosion of orifice valves is experienced during the time the valve is only partly open. For example, erosion is most significant when the valve is in a range of positions from being "cracked open", i.e., just slightly open, to a position providing about 25% of the maximum flow through the valve.
When the valve is in this range of positions, a relatively high velocity fluid stream can be directed through holes in the disks toward the wall of the valve body. As the high velocity stream impinges on the wall, it causes rapid erosion. Abrasive fluids have been known, for example, to erode completely through the wall of an orifice valve in as little as several hours.
When the degree of erosion is severe, e.g., when the wall of a valve body has a hole formed in it from impingement of a fluid stream, oil well production must be stopped while the valve is replaced. Both the down time caused by valve replacement and the expense of the valves results in a significant increase in the cost of recovery of petroleum products.
Erosion is in part avoided by providing orifice valves made in part of erosion-resistant materials. These materials can be ceramic materials or metals such as tungsten carbide and the like.
However, even when erosion-resistant materials are used, the rate of erosion and resulting frequency of valve replacement is still much higher than desired.
The cost of petroleum products is increasing at a rapid rate. It is, therefore, desirable to provide an orifice flow control valve which requires a minimal frequency of replacement, resulting in less down time of well systems for improving economics of petroleum recovery.